One of semiconductor manufacturing apparatuses, there is a vertical thermal processing apparatus that thermally processes a number of semiconductor wafers (hereinafter referred to as “wafers”) in block (batch). As shown in FIG. 11, for example, the vertical thermal processing apparatus includes a charge/discharge area through which a carrier, not shown, accommodating a plurality of wafers is carried to and from the outside. The wafers in the carrier are transferred by a transfer apparatus 11 to a wafer boat 12 capable of holding a number of wafers 1 in a tier-like manner. By loading the wafer boat 12 to a thermal processing furnace, not shown, a predetermined thermal process is simultaneously performed to the wafers 1.
The transfer apparatus 11 includes: a base table 13 capable of being elevated and lowered, being rotated about a substantially vertical axis, and of being substantially horizontally moved; and forks 14 for holding a plurality of, e.g., five wafers 1, the forks 14 being capable of being moved along the base table 13. For example, five wafers 1 can be transferred and transferred in batch by, e.g., the five forks 14 between the carrier and the wafer boat 12. As shown in FIGS. 11 and 12, for example, the wafer boat 12 has: a plurality of columns 15; a number of holding parts 16 (see, FIG. 12) formed in the columns 15 for holding peripheral portions of wafers, which are spaced at predetermined intervals therebetween in the up and down direction; and ring members 17 interposed between the holding portions 16 adjacent to each other in the up and down direction.
In the carrier, wafers are also held with their peripheral portions by not-shown holding parts, with predetermined intervals between the wafers adjacent to each other in the up and down direction. As shown in FIG. 12(a), the wafers 1 are received from the carrier and the wafer boat 12 in the following manner. At first, the respective five forks 14 are inserted to spaces below the wafers 1 held by the carrier or the wafer boat 12, and the forks 14 are elevated so as to float up the wafers 1. Then, the wafers 1 are received by the respective forks 14 and the forks 14 are retracted, whereby the wafers 1 are received from the carrier or the wafer boat 12. Thereafter, the wafers 1 are transferred by the transfer apparatus 11 to an object to which the wafers 1 are to be transferred.
In the wafer boat 12, there is a demand for holding wafers 1 as many as possible in order to improve a throughput of a process, and thus pitches between the wafers 1 arranged in the wafer boat 12 tend to be narrowed. In particular, in the wafer boat 12 of a type in which the ring members 17 are interposed between the wafers 1 adjacent to each other in the up and down direction, there is a case in which a pitch interval between the wafers 1 is smaller than 10 mm. Since the wafers 1 and the ring member 17 are arranged in this narrow space, when the fork 14 is moved into (or retracted from) the space between the wafer 1 and the ring member 17, a clearance between the fork 14 and the ring member 17 in the up and down direction is smaller than 1 mm. On the other hand, although the wafer boat is generally made of quartz, when a process temperature exceeds, e.g., 1000° C., the wafer boat 12 is deformed by the thermal effect, so that the clearance may differ from the clearance upon teaching. The following reasons are considered for this deformation. Namely, since a succeeding process is started before the thermally expanded wafer boat 12 is not sufficiently cooled, the wafer boat 12 is subjected again to a thermal effect without the deformed wafer boat 12 returning to the original state. In addition, since the ring member 17 is larger than the wafer, the ring member 17 is vulnerable to the thermal effect, and is likely to be lowered by its own weight from a set position. As the number of the process increases, the degree of the deformation becomes serious because of these reasons.
Suppose that the clearance differs from the clearance upon teaching. As shown in FIG. 12(b), when the wafer 1 is transferred by the fork 14, there is a possibility that the wafer 1 and the fork 14 might come into contact with each other so that the surface of the wafer 1 might get scratched, and that the wafer 1 and the fork 14 might come into contact with each other so that the transfer of the wafer 1 cannot be performed.
Citation 1 describes a vertical thermal processing apparatus including a substrate holder capable of holding a plurality of objects to be processed in a tier-like manner in the up and down direction, and a transfer mechanism that transfers objects to be processed to the substrate holder, wherein information as to a feedback position, a velocity, and a current of a motor for driving the transfer mechanism are monitored, while the information and a preset information as to the normal driving state of the motor are compared to each other. Upon detection of an abnormality, the driving of the transfer mechanism is stopped. However, this technique is a countermeasure taken when the driving of the transfer mechanism become abnormal, and is not a countermeasure when the substrate holder becomes abnormal. Thus, this technique cannot solve the problem of the present invention.    [Patent Document 1] JP2007-251088A